Effects of soil nutrient availability on the development of tropical monodominance and subordinate species composition in montane forests

Although tropical forests are well known for harbouring some of the highest levels of plant diversity in the world, natural areas occur where a single tree species dominates the forest stand. The presence of these monodominant forests therefore represents an unusual and intriguing phenomenon. Several studies over the past 30 years have attempted to explain how monodominance arises and how monodominant species persist in otherwise highly diverse tropical forests. Proposed mechanisms can be grouped into the “exceptional trait” and “ecosystem modification” hypotheses. Using the framework of these hypotheses, this study aimed to understand how an ectomycorrhizal tree species, Oreomunnea mexicana, achieves high abundance. The study assessed soil properties along with species composition using a paired plot design consisting of mixed forest and nearby Oreomunnea-dominated forest sampled at four sites in montane forest in western Panama. We found support for the “ecosystem modification” hypothesis as Oreomunnea-dominated stands mostly differed in soil properties from mixed forest stands that shared the same soil parent material. Alterations to soil conditions via a positive plant-soil feedback were also associated with differences in the composition of the subordinate tree species community. Species diversity not affected by the presence of Oreomunnea, and compositional beta-diversity was lower across Oreomunnea-dominated forests, suggesting that the plant-soil feedback imposed additional environmental filtering on the tree community. However, the capacity to generate plant soil feedback is itself a consequence of an “exceptional trait”, the presence of ectomycorrhizal fungi associations in Oreomunnea-dominated forests, in a community otherwise consisting of trees that form arbuscular mycorrhizal associations

DIVERSIDAD DE ÁRBOLES Y ARBUSTOS EN LA RESERVA PRIVADA CERRO CHUCANTÍ EN DARIÉN, PANAMÁ

Cloud forests play a fundamental role in the maintenance and quality of water, in addition to generating habitats for animals. The structure and characteristic of these forests makes them "hot-spots" of biodiversity and centers of endemism. In this study the alpha diversity of a plant community was calculated, and it was evaluated in a very general way, whether the height influences the richness of species in a Cloud Forest in the Darién province. A lower species richness was expected as the height increased. For this, the diversity of trees, shrubs, palms and arboreal ferns was calculated in 0.4 ha and the species richness was evaluated by plot in two altitudinal levels. It was found that the diversity of species is very high compared to other cloud forests of the tropics, in addition, the species showed no tendencies of inequality and dominance. No influence of height on species richness was observed (p = 0.96). However, when we analyze the composition of species by zones, we find that they only share 2sp with each other. What makes us think that height does not clearly explain the species richness in Chucantí and that could be explained by other environmental factors.Los bosques nubosos juegan un papel fundamental en el mantenimiento y calidad de agua, además de generar hábitats para los animales. La estructura y característica de estos bosques los hace ser “hot-spots” de biodiversidad y centros de endemismo. En este estudio se calculó la diversidad alfa de una comunidad vegetal y se evaluó de forma muy general, si la altura influye en la riqueza de especies en un Bosque Nuboso en la provincia de Darién. Se esperaba una menor riqueza de especies a medida que aumentaba la altura. Para esto, se calculó la diversidad de árboles, arbustos, palmas y helechos arbóreos en 0.4 ha y se evaluó la riqueza de especies por parcela en dos niveles altitudinales. Se encontró, que la diversidad de especies es muy alta comparado con otros bosques nubosos del trópico, además, las especies no mostraron tendencias de desigualdad y dominancia. No se observó una influencia de la altura en la riqueza de especies (p=0.96). Sin embargo, cuando analizamos la composición de especies por zonas, solo 2 especies fueron compartidas entre sí. Lo que hace pensar que la altura no explica claramente la riqueza de especies en Chucantí y que pudiera ser explicado por otros factores ambientales

Plant size, latitude, and phylogeny explain within-population variability in herbivory

Interactions between plants and herbivores are central in most ecosystems, but their strength is highly variable. The amount of variability within a system is thought to influence most aspects of plant-herbivore biology, from ecological stability to plant defense evolution. Our understanding of what influences variability, however, is limited by sparse data. We collected standardized surveys of herbivory for 503 plant species at 790 sites across 116° of latitude. With these data, we show that within-population variability in herbivory increases with latitude, decreases with plant size, and is phylogenetically structured. Differences in the magnitude of variability are thus central to how plant-herbivore biology varies across macroscale gradients. We argue that increased focus on interaction variability will advance understanding of patterns of life on Earth